Package



Jan. 25, 1966 J. H. RYAN, JR v 3,231,079

PACKAGE Filed Jul 28, 1964 |||llllllll l|||1ll|||| I IN VENTOR JOSEPH HENRY RYAN, JR.

ATTORNEY United States Patent Office assignor to Wilmington,

This invention relates to the packaging of articles. More particularly, it relates to a package in which a pneumatic, flexible, ultramicrocellular sheet having one slickened side and one high friction side is employed to wrap and protect an article inside a shipping carton.

The prior art has provided many materials for protecting fragile articles or products with highly finished surfaces during their shipment from one location to another. These materials range all the Way from coarse fibrous batts (e.g. Wood excelsior, shredded paper, animal hair or cellulosic fibers, etc.) to custom molded, fitted, shock absorbing foam blocks. The latter, while frequently offering excellent shock absorption and surface protection, are obviously relatively expensive and require a separate invention for each different-shaped item in a product line, while the former are frequently interior in the degree of protection provided.

It is an object of this invention to provide a package which offers both shock absorption and surface protection at low cost. A further object is to provide such a package for readily accommodating articles of various shapes and sizes. A still further object is to provide such a package utilizing a shock absorbing layer which is clean, hygienic, attractive in appearance and non-dusting in use. Other objects will be apparent from the remainder of the specification and claims.

In accordance with the invention there is provided a package comprising a container having disposed therein an article wrapped in a shock absorbing covering, a first major surface of said covering being adjacent said article, a second major surface of said covering being adjacent said container and having a coefiicient of friction at least 20% less than that of said first major surface, said covering comprising a resilient, fiexibile ultramicrocellular sheet of a synthetic linear crystalline polymer wherein substantially all of said polymer is present as filmy Walls of generally polyhedral shaped cells, individual filmy Walls of the sheet being less than 2 microns in thickness, being of substantially uniform thickness, and exhibiting uniform texture, the crystallites of said polymer in individual filmy walls of the sheet exhibiting uniplanar orientation. For purposes of this invention, the coefiicient of friction is measured using as the reference surface ordinary kraft paper of the type used in corrugated carton facings.

Copending US. application SN. 170,187 filed January 31, 1962, describes extrusion of the ultrarnicrocelular foam sheets from which the shock absorbing coverings employed in this invention may be formed. The asextruded, pneumatic, inflated-cell sheets, preferably containing a quantity of impermeant inflatant in each cell, have excellent shock absorbing and cushioning properties which are most desirable in a sheet intended for wrapping articles to be packaged for shipping.

The drawing illustrates a package according to the invention. Thus the package 10 comprises shipping container 11 of corrugated paperboard or the like, a wrapping of shock absorbing covering 12 and an article 13 to be shipped, in this case shown simply as a radio. The relatively slick surface of the shock absorbing covering 12 is adjacent the inner walls of the container 11 whereas the covering surface having the higher coefiicient of friction is adjacent the article 13. The container is preferably of such dimensions that the article 13 and a single ply of covering 12 snugly fit thereinto. Of course it is not necessary, for most purposes even undesirable, that the covering 12 be cemented or otherwise adhered to either the carton 11 or the article 13. It Will be understood that the article may, if desired, include one or more other protective covers such as waxed paper, oil paper, polyethylene film, cellophane or the like. Similarly the container may have special coatings or films about its inner surface and may include spacers or inserts to help prevent shifting of the contents during shipping. Depending upon the mode of assembly or other considerations, the shock absorbing covering may comprise either a single piece of material, several such pieces, or even several wrappings.

The term uniplanar orientation employed with respect to the ultramicrocellular sheets may be fully understood from the following discussion. Axial, planar, and uniplanar indicate different types of molecular orientation of high polymeric materials. Axial orientation refers to the perfection with which the molecular chains in a sample are aligned with respect to a given direction, or axis, in the sample. For example, prior art filaments which have been drawn only in one direction generally exhibit an appreciable degree of axial orientation along the stretch direction. Planar orientation refers to the perfection with which the molecular chains are oriented parallel to a surface of the sample. Uniplanar orientation as possessed by the ultromicrocellular sheets is a higher type of polymer orientation in that it refers to the perfection with which some specific crystalline plane (which must include the molecular chain) in each polymer crystallite is aligned parallel to the surface of the sample. Obviously, only crystalline polymers can exhibit uniplanar orientation. These three types of molecular orientation may occur singly or in combination; for example, a sample might simultaneously exhibit I microcellular structures.

and hence are directly useful as protective padding (e.g.

athletic equipment pads, wrestling mats, bumper pads in livestock transporting vehicles, etc.), rug underlayment, spring-insulator pads in upholstered furniture or mattresses, etc. The unique combination of the microstructural elements of these ultramicrocellular samplesthe polyhedral cells, the uniform texture of the cell walls, and the high degree of perfection of crystallite uniplanar orientationall cooperate to provide a sheet possessing extraordinary tensile properties and pneumatic shock absorption combined with the flexibility and conformability uniplanar and axial orientation.

Electron diffraction furnishes a convenient technique for observing the presence of uniplanar orientation in the A single cell Wall is placed perpendicular to the electron beam. Since the Bragg angle for electron diffraction is so small, only crystalline planes essentially parallel to the beam (perpendicular to the Wall surface) will exhibit diffraction. If the sample does in fact have perfect uniplanar orientation, there is some crystallographic plane which occurs only parallel to the film surface and, therefore, will be unable to contribute to the diffraction pattern. Thus, the observed pattern will lack at least one of the equatorial diffractions normally observed for an axially oriented sample of the same polymer. If the degree of uniplanar orientation is somewhat less than perfect, there may be a few crystallites tilted far enough to contribute some intensity to the diffraction pattern, but at least one of the equatorial diffraction intensities will be appreciably less than normal. Thus a sample is considered to have uniplanar orientation when at least one of the equatorial diffractions appears with less than one-half its normal relative intensity as determined on a standard which is a randomly oriented sample of the same polymer. A simple Patented Jan. 25, 1.966

standard for this purpose is a thick inflated portion of the same ultramicrocellular structure, since the total array of many walls averages out to random orientation; necessarily the intensities will be determined on a diffraction pattern made using an X-ray beam because of the increased sample thickness for such a standard.

An alternative and occasionally more convenient technique for detecting the presence of uniplanar orientation in a sample is to observe the electron diffraction pattern as the plane of the sample is tilted with respect to the electron beam. (In case the sample also exhibits axial orientation, the tilt axis is preferably parallel to the orientation axis.) For uniplanar-oriented samples, first one crystallographic diffraction plane and then another will assume the position required for Bragg diffraction so that first one and then another lateral diffraction will appear and then disappear as the sample rotation continues. The more perfect the degree of uniplanar orientation, the more sharply defined is the angle at which any particular diffraction appears. When a plot of diffraction intensity (corrected for sample thickness variation) vs. angle of sample tilt is prepared for any of the lateral difiractions, the distance in degrees tilt between points of half-maxi mum intensity may be readily determined. Only samples having uniplanar orientation will have half-maximum intensity points separated by 90 or less, and this will serve as an alternate criterion for the presence of uniplanar orientation.

One precaution must be observed in making this measurement. If the sample field examined by the electron beam is stopped down so far that it sees only one crystallite at a time, it will always be possible, even for a randomly oriented sample, to find some crystallite oriented parallel to the sample surface which would, of course, give an uniplanar orientation diffraction pattern. In order to insure that the uniplanar orientation pertains to the whole film element and not just to one crystallite, the measurement should be made examining a field of 100 square microns area or so, which is large enough to include the contributions from many crystallites simultaneously. Other techniques of measuring uniplanar orientation and their co-relation with electron diffraction measurements are described in the J. Pol. Sci. 31 335 (1958) in an article by R. S. Stein.

The term uniform texture applied to the polymer in the cell walls means that the orientation, density, and thickness of the polymer is substantially uniform over the whole area of a cell wall, examined with a resolution of approximately /2 micron. This is best determined by observing the optical birefringence in the plane of a wall of a cell removed from the sample. For ultramicrocellular samples with a net over-all axial orientation, the individual cell walls will also normally exhibit an axial orientation in addition to the required uniplanar orientation. In the birefringence test, such products will show a uniform extinction over the whole area of the cell wall. Samples with no net axial orientation must show a uniform lack of birefringence over their whole area rather than numerous small patches of orientation with each patch oriented at random with respect to the others. Lacy or cobweb-like cell walls, of course, do not have uniform birefringence over the whole area of a cell wall,

the identity of the polymer and the conditions of cell formation are known. Otherwise the closed-cell content of a yieldable sample may be determined by the gas displacement method of Remington and Pariser, Rubber \Vorld, D/Iay 1958, p. 261, modified by operating at as low a pressure differential as possible to minimize volume changes of the yieldable closed cells.

The cell Wall thickness can be determined by microscopic examination of cross sections. Thus 20-60 micron thick sections may be cut from a frozen sample with a razor blade. Large cell 50 microns) samples are frozen directly in liquid nitrogen. Smaller celled samples are preferably imbedded in water containing a detergent, and then frozen and sectioned. The transverse dimensions of one or more cells can also be readily measured by freezing and sectioning techniques. The cells are found to exhibit a general polyhedral shape, similar to the shape of the internal bubbles in a foam of soap suds. The ultramicrocellular sheets should have cell dimensions which are small compared to the thickness dimension of the product. For this reason the average transverse dimension of the cells in expanded condition should be less than 1000 microns, preferably less than 300 microns, and the mutually perpendicular transverse dimensions of a single cell in a fully inflated condition should not vary by more than a factor of three. The ratio of the inflated cell volume to the cube of the wall thickness can be calculated and exceeds about 200. For very thin walled samples 1 micron), the wall thickness is preferably measured with an interferometer microscope. A layer of the sample is peeled off by contact with Scotch tape. The layer is freed from the tape by immersion in chloroform and subsequently placed on the stage of the microscope for measurement.

In the packages of the present invention, the ultramicrocellular sheet of the shock absorbing covering provides tensile strength, pneumaticity, flexibility and conformability as well as the important frictional differential, i.e. the sheet possesses on one surface a coefficient of friction substantially less than that of the other surface. As used herein the coefficient of friction refers to the dynamic coefficient of friction as determined by the classic-a1 method of measuring the force required to maintain relative motion at the interface between the test surface and a specified reference surface. The data exhibit the expected independence of load and velocity of motion, and the coefficients of friction quoted hereinafter have therefore been measured at arbitrarily chosen values of 12 grams per cm. and 10 inches per minute. As above mentioned, the reference surface for the measurements is kraft paper.

The required surface slickening may readily be accomplished, for example, by ironing one surface of the pneumatic ultramicrocellular sheet, singeing one surface with a flame in a conventional fabric singeing machine, or passing the sheet through a differentially-driven, oneside-heated calender. It has also been found that the high tensile strength, stretch-collapsed ultramicrocellular and such products are readily distinguished from the unisheet produced according to the coupled extrusion stretch-collapsing process of copending application S.N. 326,444, filed November 27, 1963, has a low coefficient of friction on both surfaces as compared to the sheet before stretching. Such a stretch-collapsed sheet, which is relatively nonpneumatic, can be laminated to an uncollapsed pneumatic ultramicrocellular sheet to yield a most dsirable package cushioning laminate having excellent tensile strength and shock absorbing properties, flexibility and conform'ability, and the required slick-andstick surface properties (contributed by the collapsed and normal sheet surfaces of the laminate, respectively). Other laminates of pneumatic ultramicrocellular sheets to suitably treated films, foils and papers will yield equally satisfactory products.

In use, the shock absorbing coverings are wrapped around the articles to be protected (e.g. a piece of finished wood furniture, a glass object, cast plastic, or highly polished metal), slick-side-out, and the whole enclosed in a shipping container, which is ordinarily a corrugated kraft carton. The function of the slick-andstick surfaces of the sheet is to insure that any shifting of the article relative to the carton which occurs during the normal vibrations and shocks to which the carton is exposed will occur at the interface between the slick surface of the sheet (the one with the lower coefiicient of friction) and the carton rather than at the surface of the article (which is adjacent the sheet surface with the higher coefiicient of friction). This avoids undesirable abrading ,or polishing of the highly finished surface of the article during shipping. It will be apparent that some advantage will be achieved when any degree of slickening of the outer surface of the sheet is effected in comparison with the inner sheet surface which will contact the article to be protected. Similarly the higher the degree of slickening, the more desirable and effective is the product. It has been determined experimentally that to create a slick-and-stick sheet product wherein essentially all the sliding motion occurs between the slickened surface and the carton, the slickened surface should have a coefficient of friction (as measured vs. kraft paper) at least 20% less than that of the opposite surface. Surprisingly the 20% relative difference in coefficient of friction between the two sheet surfaces will act to confine most of the shifting action between the sheet and the shipping container essentially irrespective of the level at which the values occur. Similarly it matters very little that the outside of the article and the inside of the container may differ considerably in their own coefficients of friction.

Another advantage of the outer slickened surface of the shock absorbing covering is that it facilitates insertion of the wrapped article into the carton, as well as the subsequent insertion of any required filler or spacer blocks. Still other advantages provided by the ultramicrocellular sheets which comprise the coverings are their completely inert nature (no plasticizer or residual solvents to attack or soften the finishes of the packaged articles), their soft non-abrading surface, their non-dusting character, their immunity to mildew and rot, the additional protection they offer the packaged article from water damage, their exceedingly light weight, and of course their shock absorbing properties. These pneumatic ultramicrocellular sheets have a further unique advantage in that the coefficient of friction between their untreated surface and lacquered wood or plastic is frequently as large as 3 or greater. This is uncommonly high for a nonabrasive, non-tacky, compliant soft material, and greatly facilitates the ability of these sheets to cling to the surface to be protected without causing any damage thereto.

The following examples illustrate packages employing the slick-and-stick pneumatic shock absorbing ultramicrocellular sheets. All proportions are by weight unless specified otherwise.

Example I Extrusion of a pneumatic ultramicrocellular sheet is accomplished by charging a heated 2" screw extruder with linear polypropylene of melt flow No. 4.0 and a 90/10 mixture of fluorotrichloromethane/1,1,2-trifluoro- 1,2,2-trichloroethane at such a rate as to produce a 50% polymer solution. Also 0.5% (based on polymer) of a silica aerogel is added as a bubble nucleation assistant. This mixture is heated and blended in the extruder to produce a homogeneous solution which is accumulated under pressure in a holding vessel. The temperature of the solution is adjusted to 140 C. and the solution extruded under a pressure of 360 p.s.i.g. through a nominal 9" perimeter annular blown-film die with a 5 mil gap. Flash vaporation of the halogenated methane and ethane compounds when the solution is extruded into the atmospheric pressure region outside the vessel immediately generates a continuous ultramicrocellular tubular product and quenches the polyhedral shaped cellular material to a stable state exhibiting uniplanar orientation and uniform texture. The gas pressure confined inside the tubular sheet in the region between the die face and downstream pinch rolls (which flatten the tube to a double sheet) is increased until the tube is laterally expanded just enough to prevent longitudinal pleat formation. The tubular sheet is subsequently slit longitudinally, spread to a single thickness, and rolled up. The gas-filled polyhedral cells contribute a pneumatic character to this sheet. it is flexible and conformable, has a thickness of approximately 0.04, and a tensile strength of 2.5 lbs./in. (machine direction) at a basis weight of only 0.4 oz./yd.

A length of this sheet is unwound, the upper surface temporarily covered with a thin sheet of fluorocarbonresin-coated glass fabric to prevent sticking, and then ironed with .an ordinary household iron set to the wool temperature. This treatment reduces the coeflicient of friction of the ironed surface by 39% with the result that only as much force is required to maintain motion between the ironed surface and a kraft paper surface as is required to maintain motion between the untreated surface and a lacquered wood surface. In contrast, when a commercial package cushion-ing material comprising a carded cotton batting backed with 30 lb. kraft paper is used between the wood and kraft paper (the latter simulating a corrugated carton surface), the two interfaces have almost equal mobility.

Several lacquer-finished wooden-cabinet stereo phonograph sets are each wrapped with a single thickness of the slick-and-stick pneumatic ultramicrocellular sheets, slick-side out, and then covered with a corrugated shipping carton which is sealed with staples. These packages are placed up-side-down (i.e. so that the phonograph is supported in the carton on its polished top surface) on a vibrating table tester which is run for 1% hours. This test is considered to offer a critical prediction of shipping performance. No discernible damage to the fine furniture finish can be observed on unpacking the sets.

In a subsequent test, four such sets are packaged in a similar manner, one pair employing slick-and-stick pneumatic protective sheets, and the other pair employing untreated pneumatic sheets. These sets are shipped over a thousand miles. Every set survived shipment undamaged and free from imprint marking by the corrugated container, attesting to the excellent shock absorption protection afforded by the pneumatic sheets. However, the two untreated-sheet-wrapped sets suffered a light dulling of the lacquered finish, apparently from relative motion at the sheet/set interface. The two sets protected with the slick-and-s'tick sheets according to the invention survived with the finish in its original high gloss condition.

The basis weight for the paper/ cotton batting cushioning material typically employed for such a use is approximately 4.5 oz./yd. While the ultramicrocellular sheets employed in the above test have a basis weight of only 0.4 oz./yd.

Example II In this example, the pneumatic ultramicrocellular sheet of Example I is provided with one slick surface by laminating it to a collapsed ultramicrocellular sheet prepared from linear polyethylene according to the technique of aforementioned copending application S.N. 326,444. This 0.3 oz./yd. collapsed ultramicrocellular sheet is laminated to the 0.4 oz./yd. pneumatic sheet with a rubber base adhesive to produce a slick-and-stick package cushioning sheet of overall basis weight 0.9 oz./yd. Spencer puncture of 1.0 in.-lb./in. and ratio of coefficients of friction (stick-side/slick-side) of 0.54/0.25, Le. a reduction of 54%.

These laminated sheets are employed to package four wooden stereo cabinets directly on a commercial production line. The cabinets are wrapped with a single thickness, slick-side-out, and covered with a corrugated paperboard carton into which the normally-used tight-fitting corrugating inserts are placed to help prevent shifting during shipping. These cartons are shipped a substantial distance from the cabinet manufacturer to the electronic manufacturer where the cabinets were unpacked and found to be free from any shipping damage, and the laminated cushioning sheets still intact. This test demonstrates several points: the factory-fresh lacquered finishes are not marred by the sheets, the sheets furnish adequate shock protection during shipping, the sheets furnish superior surface-abrasion protection during shipping, and the sheets have adequate tensile strength (due to the unique microstructure of the cells) to survive commercial packaging and shipping operations.

Example III A pneumatic ultramicrocellular linear polypropylene sheet is extruded as in Example I, excepting only that the polymer concentration was 45% instead of 50%. The 0.4 oZ./yd. sheet is slickened on one surface by the ironing technique of Example I. A clock radio with a molded polystyrene case is wrapped with this sheet, packed in a corrugated carton and shipped via parcel post a distance of some two hundred miles whereupon the radio is unpacked, examined, re-packed and re-shipped a similar distance. On final inspection at the point of receipt, the delicate polystyrene case was found free from unacceptable damage, even though the carton showed evidence of rough handling in transit.

In contrast with the excellent performance of the package of this invention in this application, cellulose wadding material in a commercial package is found to scratch the molded polystyrene case, while cushioning sheets of ordinary commercial foamed polystyrene (prepared from expandable polystyrene beads) prints the residual bead pattern or the polystyrene case, perhaps due to attack by the residual plasticizer or blowing agentfrom the originaltherein an article wrapped in a shock absorbing covering.

a first major surface of said covering being adjacent said article, a second major surface of said covering being adjacent said container and having a coefficient of friction at least 20% less than that of said first major surface, said covering comprising a resilient, flexible ultramicrocellular sheet of a synthetic linear crystalline polymer wherein substantially all of said polymer is present as filmy walls of generally polyhedral shaped cells, individual filmy walls of the sheet being less than 2 microns in thickness, being of substantially uniform thickness, and exhibiting uniform texture, the crystallites of said polymer in individual filmy walls of the sheet exhibiting uniplanar orientation.

2. The pack-age according to claim 1 wherein the surfaces of said covering are surfaces of said ultramicrocellular sheet.

3. The package according to claim 1 wherein said covering is a laminate comprising said ultramicrocellular sheet.

4. The package according to claim 1 wherein said container is a corrugated paperboard carton.

5. The package according to claim 1 wherein said synthetic linear crystalline polymer is polypropylene.

References Cited bythe' Examiner UNITED STATES PATENTS 2,784,131 3/1957 Fletcher 2,917,223 12/1959 Le Bolt et al. 2,979,246 4/1961 Liebeskind 229-l4 FOREIGN PATENTS 1,157,061 12/1957 France.

848,248 9/1960 Great Britain.

856,558 12/ 1960 Great Britain.

THERON E. CONDON, Primary Examiner. 

1. A PACKAGE COMPRISING A CONTAINER HAVING DISPOSED THEREIN AN ARTICLE WRAPPED IN A SHOCK ABSORBING COVERING, A FIRST MAJOR SURFACE OF SAID COVERING BEING ADJACENT SAID ARTICLE, A SECOND MAJOR SURFACE OF SAID COVERING BEING ADJACENT SAID CONTAINER AND HAVING A COEFFICIENT OF FRICTION AT LEAST 20% LESS THAN THAT OF SAID FIRST MAJOR SURFACE, SAID COVERING COMPRISING A RESILIENT, FLEXIBLE ULTRAMICROCELLULAR SHEET OF A SYNTHETIC LINEAR CRYSTALLINE POLYMER WHEREIN SUBSTANTIALLY ALL OF SAID POLYMER IS PRESENT AS FILMY WALLS OF GENERALLY POLYHEDRAL SHAPED CELLS, INDIVIDUAL FILMY WALLS OF THE SHEET BEING LESS THAN 2 MICRONS IN THICKNESS, BEING OF SUBSTANTIALLY UNIFORM THICKNESS, AND EXHIBITING UNIFORM TEXTURE, THE CRYSTALLITES OF SAID POLYMER IN INDIVIDUAL FILMY WALLS OF THE SHEET EXHIBITING UNIPLANAR ORIENTATION. 